In the related art, a technique of estimating a distance from a mobile terminal device to an object, for example, using a radio communication technique such as Bluetooth (registered trademark) is known. Specifically, a beacon that emits radio waves is attached to an object and the radio waves emitted from the beacon are received, for example, by a mobile terminal device or the like carried by a user. The mobile terminal device estimates a distance from the mobile terminal device to the beacon on the basis of radio field intensity of the received radio waves.
Estimation of an arrival direction of a radio wave emitted from a beacon is also considered to search for a location of an object. That is, a detector including, for example, an antenna that can switch its directivity receives radio waves while switching the directivity of the antenna and estimates arrival directions of radio waves on the basis of a variation in radio field intensity. Accordingly, since a distance to and a direction of a location of a beacon are estimated, it is possible to specify the location of the object to which the beacon is attached.
Patent Document 1: Japanese Laid-open Patent Publication No. 2014-99857
Patent Document 2: Japanese Laid-open Patent Publication No. 2005-207837
Patent Document 3: Japanese Laid-open Patent Publication No. 2004-334439
However, there is a problem in that it is difficult to search for a location of an object using a mobile terminal device which is generally spread such as a smartphone. That is, when a mobile terminal device such as a smartphone is used, it is possible to relatively easily estimate a distance to a beacon, but it is difficult to estimate a direction of the beacon. This is because a mobile terminal device such as a smartphone does not generally have a function of switching directivity and has a difficulty in estimating an arrival direction of a radio wave emitted from a beacon.
Accordingly, a special detector equipped with an antenna that can switch directivity or the like is used to search for a location of an object using a radio communication technique, thereby causing a decrease in convenience or an increase in cost.